1. Field of the Invention
This invention relates to serial impact printers and more particularly, to serial impact printers incorporating a shared character selection system, print carrier escapement system and print line advance system.
2. Description of the Prior Art
Prior art serial impact printers and typewriters employing a single element typefont often utilize separate drive systems for driving the typefont along the print line and for driving the typefont to select a particular character for subsequent impact printing. A still further drive system is utilized for the line advance function. This approach is generally costly, not only because of the cost of the independent drive systems employed, but also because such a design approach necessitates heavier duty components. For example, conventional daisy wheel printers use a first motor located on the daisy wheel print carrier to rotate the daisy wheel to effect proper character selection. Since the print carrier is serially moved along the print line from character position to character position, and since the selection motor adds great relative weight to the print carrier, a more powerful motor and print carrier drive system have to be utilized to effect print carrier escapement.
An additional prior art approach utilizes a common drive motor source to drive the character selection system and to drive the print carrier escapement system. Generally, a double clutching arrangement is utilized so that the character selection system is decoupled from the drive source during print carrier escapement and the escapement system is decoupled from the drive source during print character selection. Such double clutching schemes result in slower printing speeds. Since the character selection system must be precise, and since the escapement system generally represents a much greater load on the drive source than that of the character selection system, complex mechanisms are also necessitated to effect the sharing of the common drive source.
An additional prior art approach is described in the IBM Technical Disclosure Bulletin article of July, 1980 at page 437 entitled "Impact Printer With Carrier and Character Selection Apparatus Driven Off The Same Motor". This article describes the use of a single belt to drive both a character selection system and a print carrier escapement system from a single stepper motor. The double clutching arrangement heretofore alluded to is employed to insure engagement of only one of the loads at any given time. The constant coupling and uncoupling of the character selection system from the timing belt can lead to synchronization problems between the timing belt and the print wheel or typefont associated therewith and also slows printing speeds.